THE SULFUR BACTERIA 113 



(h) The Sulfur Bacteria 



We include in this classification the autotrophic bacteria which 

 utilize hydrogen sulfide, elementary sulfur, thiosulfate, and thiocyanate. 



Hydrogen Sulfide Oxidizers, e. g., Beggiatoa (Vinogradsky 1887), 

 transform hydrogen sulfide into sulfur globules deposited inside the cell. 

 When the sulfide is exhausted, the sulfur globules are consumed by 

 further oxidation to sulfate: 



(5.21) O2 + 2 (H2S)aq. > 2 H2O + 2 S + 126 kcal 



(5.22) O2 + f S + ! HoO > I (S04)aq-. + f H+q. + 98 kcal 



Sulfur Oxidizers (e. g., Thiohacillus thiooxidans, Waksman and Joffe, 

 1922). — These bacteria oxidize externally supplied sulfur to sulfate, in 

 accordance with equation (5.22), and are characterized by extreme 

 tolerance to acid. Their optimum pH hes between 3 and 4, and they 

 survive even in 5% sulfuric acid. 



The metabolism of these organisms recently was investigated by 

 Vogler and Umbreit. Vogler and Umbreit (1941) and Umbreit, Vogel 

 and Vogler (1942) proved that sulfur is first dissolved in fat globules in 

 the ends of the cell, and saw in this fact a proof that only oxidations 

 which take place inside the cell can provide energy for chemosynthesis. 

 According to Vogler (1942), despite its exclusively inorganic nutrition, 

 Thiohacillus possesses an organic metabolism based on storage materials 

 formed by chemosynthesis. Vogler, LePage and Umbreit (1942) showed 

 that the rate of sulfur oxidation is independent of pH (between 2 and 4.8), 

 and of the oxygen pressure; it is inhibited by cyanide (50% inhibition 

 at 10-4 mole/1.), dinitrophenol (50% inhibition at 1.3 X 10"^ mole/1.), 

 azide, iodoacetate, arsenite, indole and phthalate. It is affected by 

 urethane only at comparatively high concentrations (35% inhibition in 

 0.1 molar solutions). It is 50% inhibited by carbon monoxide in a 

 concentration of 80%, an inhibition which is removed by illumination. 

 All these results indicate that sulfur oxidation proceeds through the 

 intermediary of a heavy-metal enzymatic system (of the hemin type). 

 Since enzymes of this type transfer only electrons, and not oxygen atoms, the 

 oxygen in the SO4 — ions formed by B. thiooxidans must originate in water 

 and not in air, a consequence which could be checked by isotope tracers. 



The relation between sulfur oxidation and carbon dioxide reduction 

 by B. thiooxodans was studied by Vogler (1942-). Young cultures took 

 up a limited quantity of carbon dioxide even in the absence of sulfur; in 

 older cultures, this uptake was overbalanced by the carbon dioxide 

 production by endogenous respiration. The sulfur-free carbon dioxide 

 uptake could, however, be observed in all cultures, if respiration was 

 suspended by depriving the cells of oxygen. The maximum total uptake, 

 reached in about two hours, was of the order of 0.4 ml. of carbon dioxide 



